1. Technical Field
The present invention is directed generally toward data processing computer systems, and more particularly, to transfer of data to and from a host system and one or more input/output devices with an input/output controller.
2. Description of the Related Art
The use of the microprocessor and its bus architecture in a computer system are well known. Peripheral devices are coupled to a bus and can provide various functions related to the computer system.
Typical computer systems comprise can be broken down into three main subsystems: main memory, one or more host processors or CPUs, and an input/output (I/O) subsystem. In order to provide communication between the host processor and a plurality of external input/output (I/O) devices, it is effective for data processing systems to utilize an intermediate control unit, also known as an I/O controller.
The I/O controller facilitates interchange of data between a computer system and remote peripheral devices. As a result, I/O controllers relieve the main host processor of many of its operating cycle obligations for ensuring that data exchanges between various remote peripheral devices and the main host processor system is accomplished with minimal interruption to the main host processor.
In most conventional systems utilizing such an approach, the host processor supplies an appropriate command to the I/O controller. The I/O controller then interprets the commands so that the selected I/O device can be identified and the appropriate data processing and transfer operations can occur. The host normally supplies such commands in sequence and the I/O processor processes such commands in such sequence. If the I/O processor is busy with a particular command requiring the servicing of a specified I/O device, then the host must wait until that process is complete before it can issue subsequent commands related to either the same or a different I/O device.
Within many kinds of IO controllers, multiple different processors are often employed. When the controller receives an input/output request, one of the processors routes the request to lower level processors, or context managers, that complete the input/output request. Depending on the task the host system is accomplishing, the input/output rate can vary greatly. At times when input/output request rate is high, all processors of the controller are in use. When input/output request rates are low, some or all of the processors of the controller may not be in use at all times. However, typical systems require that unused I/O processors sit idle waiting for new I/O requests to process, consuming substantially the same average power as if they were in use. It would be advantageous to provide a controller wherein average power consumption is decreased when the processors are not needed.